ADEOS-II is a Japanese (JAXA, formerly NASDA) Earth environmental observation satellite, a successor mission to ADEOS with international cooperation. Overall objectives are to provide and improve Earth observation services with advanced payload instruments.

The science objectives of ADEOS-II are to acquire data contributing for international global change research (carbon cycle and the water and energy cycle), as well as for applications in such fields as meteorology and fishery. ADEOS-II is the Japanese contribution in the framework of the International Earth Observation System (IEOS). Other parts of IEOS are EOS (USA), and the ENVISAT and MetOp programs of ESA and EUMETSAT, respectively. The ADEOS-II mission, also referred to as Midori-II, is dedicated to the following programs: WCRP/GEWEX & CLIVAR, IGBP and GCOS. 1)2)3)

The ADEOS-II S/C, built by Mitsubishi Corporation, employs the general design of ADEOS to reduce costs. Dimension of main S/C body: approximately 6 m x 4 m x 4 m. S/C mass = 3700 kg, payload mass = 1300 kg, power = 5.3 kW (EOL), launch vehicle = H-IIA rocket, launch site = TNSC (Tanegashima Space Center). Attitude and Orbit Control: The AOCS (Attitude and Orbit Control Subsystem) employs a three-axis strap down attitude detection system and zero momentum attitude control system achieving an attitude pointing error of < 0.3º. A GPS receiver provides onboard timing and orbit position services. The design life of the spacecraft is three years minimum with a goal of five years (propellant).

The ADEOS-II spacecraft consists of a mission module, equipped with observation instruments, and a bus module where the avionics subsystems are mounted (Table 1).

S/C subsystem

Short description

C&DH (Communication and Data-Handling Subsystem)

C&DH receives and decodes command signals transmitted from the tracking control and communicates them to all the ADEOS-II instruments. It is also capable of editing the temperature, voltage, and status of the interior of each instrument and transmitting the information to the ground station using telemetry signals.

IOCS (Inter-Orbit Communication Subsystem)

IOCS is a subsystem for data-relaying and tracking control through a data-relaying satellite (DRTS) using the S-band and Ka-band.

MDP (Mission Data Processing Subsystem)

MDP) selects the type of mission data to be transmitted, adds necessary data to mission data, edits the information into packet- or multi-format, and then transmits the information to the direct transmission system (DT) and the IOCS; it is also capable of transmitting the information to the MDR (Mission Data Recorder)

ODR (Optical Data Recorder)

The ODR is a high-speed, large-volume data recorder using an optical magnetic disk system, introduced in ADEOS-II for the first time. A large-scale recording experiment will be conducted with high-speed, high-volume data. The ODR is contained in the DT unit.

EPS (Electrical Power Subsystem)

EPS has 3 functions: to supply the bus power to each subsystem of the satellite; to manage charging and discharging of the battery; and to control ignition of the ordnance controller. During an eclipse of the orbit, it supplies power to the satellite by discharging the battery. During the sunlit orbit, excess power generated by the solar paddle is used to charge the battery. During the critical phase, which is the initial stage after the launch, it provides power to ignite the ordnance controller through the explosive-tube control unit (ODC) to deploy the solar paddle, DCS antennae, and IOCS compartment as well as to release locks on AMSR and SeaWinds.

PDL (Paddle Subsystem)

PDL converts solar energy into electric energy and transfers it to the satellite's power system. The paddle system to be installed on ADEOS-II is sufficient to satisfy demands. It has a large power-generating capacity of at least 5 kW (EOL), is highly storable, has been light-weighted. The system uses an extension method wherein 50 flexible blankets with a total of 55,680 solar-battery cells are extended on a jointed mast in orbit.

AOCS (Attitude and Orbit Control Subsystem))

AOCS has four functions: to establish the three-axis attitude control after the rocket is separated from the satellite, to maintain the satellite's attitude, to control the orbit, and to articulate the solar paddle. Sensors to detect the attitude include a control-standard unit (IRC), an Earth sensor (ESA), and a fine sun sensor assembly (FSSA), Actuation is provided by a reaction wheel assembly (RWA) and a magnetic torquer system (MTQ). The latter also transmits control signals necessary for attitude control and orbit control to the RCS.

RCS (Reaction Control Subsystem)

RCS generates propulsion power necessary for initial-stage attitude correction and orbit control according to the control signals from the AOCS, using the 1 N thruster and 20 N thruster.

DTL (Direct Transmission Subsystem for local users)

DTL is capable of modulating data extracted from four (three visible and one infrared) of the 36 observation bands of the GLI (Global Imager) into BPSK; it is also capable of transmitting the data to local users such as vessels in the UHF band (467.7 MHz). The water color and water temperature data are used to study the ocean conditions, distribution of water temperature, and basic productivity of the ocean.

Table 1: Overview of the S/C avionics subsystems allocated to the bus module

RF communications: Mission data are downlinked in X-band to ground receiving stations. The S-band is used for TT&C support. In addition there is communication link via DRTS (Data Relay and Test Satellite) in Ka-band for mission data and S-band for TT&C data. This communication link is referred to as IOCS (Inter-Orbital Communication Subsystem).

Launch: A launch of ADEOS-II on a H-IIA vehicle took place on Dec. 14, 2002 from TNSC (Tanegashima Space Center), Japan, along with FedSat of Australia, WEOS of the Chiba Institute of Technology (Chiba, Japan), and MicroLabSat of JAXA, NICT and CRL as secondary payloads on the mission.

The ADEOS-II mission was operational for only 10 months - when an anomaly stopped all further operations on Oct. 24, 2003. Indeed a great loss in Earth observations for Japan and its partners as well as for the entire Earth observation community.

• On Oct. 24, 2003, ADEOS-II experienced a severepower failure, stopping all mission operations. JAXA formed immediately the “Midori-II anomaly investigation team.” However, the nature of the failure prevented any recovery that would have led to a continuation of the mission. 4)5)6)

One of the two main working hypotheses into its cause was that a debris impact on the high-power harness carrying current between the single solar array and the satellite bus resulted in a sustained electric arc. The harness consisted of a bundle of wires covered by a sheet of multi-layered insulation (MLI). 7)

• NASDA successfully conducted the intersatellite communication experiment between ADEOS-II and ARTEMIS (Advanced Relay and Technology Mission) of the European Space Agency (ESA) from March 28 to 30, 2003. This experiment used both links for data transmission; the Ka-band (26 GHz) for payload data and the S-band (2 GHz) for TT&C services.

• A successful communication experiment between ADEOS-II and DRTS (Data Relay Test Satellite) took place on Feb. 19, 2003. 8)

AMSR is a passive NASDA core sensor of MSR heritage flown on MOS-1 and MOS-1B satellites. Objectives: measurement of sea surface temperature (SST), soil water content (moisture), sea wind speed, water equivalent of snow cover, precipitation intensity, sea ice distribution, precipitable water, etc. Microwave emission from the atmosphere, ocean, sea ice, and land are measured at multiple frequencies. From this information a number of geophysical data related to the Earth environment, such as water vapor content, water content of clouds, water equivalent of the snow cover, etc. are measured. - A further instrument, AMSR-E, was developed by NASDA, it is flown on NASA's Aqua mission. 10)11)

AMSR is an eight-frequency, total-power microwave radiometer (a passive sensor) with dual polarization (except two vertical channels in the 50 GHz band). It detects microwave emissions from the Earth's surface and atmosphere. Conical scanning at 40 rpm is employed to observe the Earth's surface with a constant incidence angle of approximately 55º (a scan drive motor rotates the antenna, rotating mass is nearly 200 kg, momentum and torque compensation is achieved with momentum wheels). Multifrequency measurements are realized by arranging multiple feed-horns, and by staggering their integration timing to compensate the differences of beam direction. The 89 GHz band has two feed horns (A/B) to permit enough sampling in the along-track direction. The AMSR 2.0 m diameter offset parabolic antenna is the largest spaceborne microwave radiometer antenna of its kind; it provides reasonable spatial resolution even in lower frequency channels.

AMSR has a high-temperature calibration source (about 340 K) and a small reflector to acquire the radiant temperature of deep space (at about 3 K). This is a so-called “external calibration scheme” was first introduced by SSM/I (Special Sensor Microwave/Imager) on DMSP satellites. Each feed horn, from 6.9-89 GHz sees the calibration sources once per scan period. In addition, extensive pre-launch characterization/calibration activities were done.

GLI is an optical NASDA core sensor of OCTS heritage on ADEOS. Objectives: Biological and physical processes, stratospheric ozone. GLI is for studying and monitoring the carbon cycle in the ocean, principally as to biological processes. Multispectral observations from the near UV to the near IR reflected solar radiation from the Earth's surface including land, ocean and clouds. Determination of chlorophyll pigment, phycobilin and dissolved organic matter (DOM) in the ocean; classification of phytoplankton according to their pigment. Measurement of sea surface temperature (SST), cloud distribution, land coverage, vegetation index, etc. 12)13)14)15)16)

GLI is a 36-channel VIS/IR radiometer/imaging spectrometer (opto-mechanical instrument) featuring a cross-track mirror and an off-axis parabolic mirror as the collecting optics and focal planes in which the detectors are arrayed in the along-track direction with spectral interference (dichroic) filters. The scan mirror rotates at 16.7 Hz. GLI can tilt the scan mirror ±20º from nadir in order to avoid sun glitter. GLI has five focal planes, two for VNIR, two for SWIR, and one for MWIR/TIR. Two VNIR focal planes have detector arrays for 13 and 10 bands respectively. Two SWIR focal planes have detector arrays for 4 and 2 bands, while the MWIR/TIR regions have one focal plane with a detector array for 7 bands. One SWIR and the MWIR/TIR focal planes are cooled to 220 K and 80 K by a multistage Peltier element and Stirling cycle mechanical cooler, respectively. The VNIR detector material is Si, the SWIR is InGaAs, the MWIR/TIR material is CMT.

GLI employs piecewise linear method with cascade amplification for signal processing on four bands in order to meet requirements for automatic observation of objects with large radiance differences (ocean color and land vegetation) exhibiting a wide dynamic range.

• SAS consists of a 1 m diameter parabolic reflector antenna mounted to a spin activator assembly, which causes the reflector to rotate at 18 rpm. The antenna spins at a very precise rate, and emits two beams about 6 degrees apart, each consisting of a continuous stream of pulses. The two beams are necessary to achieve accurate wind direction measurements. The pointing of these beams is precisely calibrated before launch so that the echoes may be accurately located on the ground from space.

• SES is the heart of the scatterometer and it contains a transmitter, receiver and digital signal processor. It generates and sends high radio frequency (RF) waves to the antenna. The antenna transmits the signal to the Earth's surface as energy pulses. When the pulses hit the surface of the ocean it causes a scattering affect referred to as backscatter.

• The CDS is essentially a computer housing the software that allows the instrument to operate. It provides the link between the command center on the ground, the spacecraft and the scatterometer. It controls the overall operation of the instrument, including the timing of each transmitted pulse and collects all the information necessary to transform the received echoes into wind measurements at a specific location on Earth.

Like ILAS, ILAS-II makes observations based on the solar occultation method (Figure 13). The solar occultation method measures the components of solar light absorbed while passing through the atmospheric layer surrounding the Earth and resolves it into spectra. The substances in the atmosphere layer may be identified and quantified through spectral resolution of absorbed light because of their specific spectral absorption characteristics. Continuous observations following the sun’s path give us a wide variety of information when sunlight passes through the atmospheric layers at different altitudes. Since sunlight passing through the atmosphere is measured at different altitudes, this provides information on the altitude distribution of the light absorbing substances in the various atmospheric layers.

POLDER-2 (Polarization and Directionality of the Earth's Reflectances):

POLDER-2 is a passive optical imaging radiometer of CNES. The instrument is an identical twin to its predecessor, POLDER-1 flown on ADEOS. By simultaneously observing the Earth's radiation in polarized light and from different viewing angles, it is focusing on several themes. POLDER's very wide field of view is also a unique asset for building up time series of measurements from space, making it possible to obtain daily global coverage. POLDER-2 acquires also ocean color measurements. 29)30)31)

The POLDER instrument is an imaging system, a radiometer/polarimeter, featuring a 2-D CCD detector array, wide field of view telecentric optics and a rotating wheel carrying spectral and polarized filters. The instrument spectral characteristics are defined in Table 6 (see also instrument description under ADEOS).

The POLDER-2 instrument has a mass of 32 kg, a size of about 800 mm x 500 mm x 250 mm, and a power consumption of 42 W.

DCS is a NASDA/CNES joint development (CNES-NASDA agreement as of 1996) referred to as Argos-Next. The DCS offers worldwide capabilities for location and environmental data collection for fixed and moving platforms. The downlink frequency of 460-470 MHz with a data rate of 200 bit/s is added to the existing Argos system. The received frequency of the DCP (Data Collection Platform) is 401.65 MHz, the data rate of the DCP = 400 bit/s. Total DCS instrument mass = 76 kg, power consumption = 60 W.

The Argos-Next instrument version offers a two-way messaging capability for enhanced service provision. So-called PMTs (Platform Messaging Transceivers) are being used by the ground segment platforms able to receive and interpret messages sent by the satellite. The new service spectrum permits for example to calibrate platform sensors and to manage duty cycle by switching terminals on and off when needed. Argos-Next also supports secure message transmissions. 32)33)

Receiving Frequency

401.65 MHz±0.0405 MHz

Receiving Signal Bit Rate

400bit/s

Receiving Signal Modulation Mode

PCM(Bi phi -L)/PM

Receiving Signal Bit Error

below 1×10-5

Transmitting Frequency

465.9875 MHz

Transmitting Power

over 5 W

Transmitting Signal Bit Rate

200 bit/s

Transmitting Signal Modulation Mode

PCM(Bi-L)/PM

UHF Antenna

Formed broad beam pattern

G/T

over -36.6 dBk

EIRP

over 27.1 dBm

Table 8: Some DCS characteristics

ADEOS-II ground segment:

The main components of the ground system, which carries out the mission operation of ADEOS-II, are (Ref. 3):

Figure 19 illustrates the overall structure of the ground system for ADEOS-II.

The ADEOS-II mission operation system is a central-core system for the mission operation of ADEOS-II, and is provided by JAXA for the EOC (Earth Observation Center). The ADEOS-II mission operation system establishes plans for the operation of mission instruments, recording and playing of MDR, etc., based on sensor operation requests by sensor-providing organizations. Furthermore, it receives mission data sent via a relay satellite or directly through X-band and prepares level-0 data for each mission instrument. It also prepares standard the AMSR and GLI products (level-1 products and higher-order products with level 2 and higher) and handles DCS data.1 The level-0 data obtained by mission instruments other than AMSR and GLI that have been processed by the ADEOS-II mission operation system will be distributed to sensor-providing organizations online or through a medium.

The mission operation system of ADEOS-II also processes AMSR and GLI 1km products on a semi-real-time basis and makes them available online to semi-real-time data users.

Finally, the feeder-link station of the ADEOS-II mission operation system functions as a back-up station that transmits commands through a relay satellite and obtains telemetry data when there is trouble or some failure at the feeder-link station of the track-control system.

The information compiled and edited in this article was provided byHerbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.